Recent years have seen the realization of home networking, i.e., networking home devices for sharing various pieces of content among them. As one form of home networking, devices including a television set and a videocassette recorder are star-connected, via one router installed in a home, to a server storing pieces of content. Within such a home network, the router is assumed to be the only device connected to an external network. The server obtains various pieces of content from the external network via this router, and stores therein the obtained pieces of content. The server can then distribute various pieces of content to the devices according to their requests. In this way, the devices can share various pieces of content among them.
In view of copyright protection, however, unlimited sharing of content is not permitted. For pieces of content whose use is limited only to devices within the home network, their distribution to devices external to the home network should be strictly prohibited. In this specification, a group that is composed of exclusive devices permitted to share content is referred to as the “AD (Authorized Domain)”. Upon every receipt of a content distribution request from a device, therefore, the server first judges whether the device belongs to the AD.
One method for the judgment uses IDs of devices belonging to the AD. This method requires the user to manually register, with the server, IDs of all the devices belonging to the AD. As one example, the TCP Wrapper can be used to realize this judgment method. In the case of the TCP Wrapper, the user manually registers, into a file named “hosts. allow”, computers having access to service provided by the server.
Reference: Sakae Kumehara “Linux Network Firewall Management Guide”, Softbank, Chapter 4.2.2